Another fix is opening up and closing the in game map. I've had this happen a few times without me able to figure out why. I run in fullscreen windowed mode on a second monitor all the time, and it still occurs. I didn't even know about the other quick fixes (alt-z and such) but I still think hitting m twice is the quickest solution for me.
This also fixes random errors I get in pitbull where textures explode over bars they shouldn't, names don't get displayed, or when something didn't update within my party properly.
I get a very similar error, though sometimes it is confined to the lower right of my screen (where my action bars are) rather than stretching the whole width of the screen. Typically the top of the error is aligned with a portion of either my raid or party interface.
I play windowed and maximised, and I use Pitbull, too. I don't recall seeing the error before I got Pitbull.
It's definitely a bug in pitbull. Yesterday I was, for the first time ever, messing around with pitbull and this would happen whenever I chose the "include player in party frame" option. It went away as soon as I unchecked the option and it has never happened prior to me installing pitbull.
I have gotten this occasionally in the last few days on the right-hand side of my screen.
It seemed directly connected with a recent update of my Ace mods, so I tend to believe it has something to do with Pitbull. It is often in relationship to the alignment of my Pitbull frames, and I do not have Recount. As I have my Pitbull party frames set up horizontal instead of vertical, I suppose that could be why I have it on one side of my screen in a different manner than the OP's screen shot.
I play windowed maximized also, and it seems to happen a lot after I zone out of a battleground--e.g. shifting from the battlegroup/arena raidgroup back into my "normal" group. Alt-tabbing seems to make it worse.
I use (and have been using for quite a while) both Pitbull and Recount and have never seen the error.
How many other ace2 addons do you use? Is it possible that Pitbull alone would not cause this bug? I'm tinking about an other addon interfering with pitbull... It happens quite often after joining a battleground.
I renamed the title of the topic to get more attention of the Pitbull users.
I have this same bug happen whenever I invite a specific member of my guild into group. He is a druid if that matters at all. I run Pitbull and I DO NOT run Recount. I update my Ace addons on a daily basis. The first time it happened was about 3 weeks ago, the last time was about 2 days ago. To fix it I do the same thing as posted before, ALT-Z, ALT-Z.
I have the same error occasionally, i'm using both recount and pitbull too.
It is definately something to do with a group, as I only get it when joining a group generally. I normally get rid of it by leaving the group and asking for a reinvite.
My guess it's one of the druids Buffs, Maybe lotp fading? (As both are druids in caster form) Or maybe they are in tree/moonkin form Most likely moonkin for, might be those buffs not being showed correctly? Try testing that by partying with a moonkin druid, and let him jump in and out of moonkin form and file a feedback form to the pitbull team.